Computer systems generally have several levels of memory; each level of memory can provide differing levels of speed, memory capacity, physical size, cost, power requirements, voltage levels and/or volatility. These aspects are often at odds with each other. For example, increases in speed often lead to corresponding increases in power requirements. For this reason, many systems use a variety of different memories within the same system. From the perspective of a computer program these memories are often hidden in the sense that common data is temporarily cached in smaller and faster memory circuits. This common data is mapped to larger and slower memory circuits, which are accessed when the faster memory does not contain the desired data. The common data, if changed in the cached memory, can eventually be written to the larger and slower memory circuits. This allows for the slower memory's access time to be avoided or hidden, so long as the faster memory contains the appropriately mapped data.
Computer systems generally contain some type of mass-storage nonvolatile memory that is able to retain stored data when the computer system is powered down. This type of memory is referred to as nonvolatile memory because it is able to maintain data integrity when the computer system is not powered. Nonvolatile memory, however, may be slower by orders of magnitude relative to various volatile memories. Yet, nonvolatile can also be less expensive (per unit of memory capacity) and/or less power-hungry. A common type of nonvolatile mass-storage memory device is a hard disc drive (HDD) that uses a rotating magnetic media for data storage. HDDs are used for home computers, servers, workstations, consumer-electronics and various other devices. Under normal operation a computer system transfers data requiring nonvolatile retention from temporary memory to a HDD before the computer system is powered down. This allows for the system's data to be retained after the power is removed from the computer system. When the computer system is subsequently powered up, this data can be accessed and used by the computer system.
HDDs with rotating magnetic media have been in use for many years and have undergone various improvements including efficiency, reliability and data storage capacity. Various applications, however, are beginning to use other types of mass data storage devices with more frequency. Solid State Drives (SSDs), using electronic nonvolatile memory, such as flash, are one such type of device, and are attractive for many applications. Speed, cost and power requirements also factor into the selection of data storage devices such as SSDs or HDDs.
While SSDs are useful in a multitude of applications, aspects of their operation and implementation remain challenging. For example, SSDs are often used in environments that have been designed for operation with other types of circuits and/or drives such as HDDs, which often operate at voltages that may or may not be amenable to use with different types of circuits. In many instances, available power sources do not necessarily match the power requirements of SSDs, or otherwise involve additional power sources that may be unused in certain circumstances, such as when design circuitry is replaced with replacement circuitry (e.g., when an HDD is replaced with a SSD). Powering SSDs in an efficient, reliable and inexpensive manner has been challenging.